1. Field of the Invention
The present invention relates to elastic wave filter devices used for band-pass filters, duplexers, or other devices, and more particularly, to an elastic wave filter device including an elastic wave filter chip that is mounted, by flip-chip bonding, on a laminated substrate in which inductance elements are included.
2. Description of the Related Art
Duplexers have been used for the RF stage of cellular phones or other communication devices in order to reduce the overall size of the device. In Japanese Unexamined Patent Application Publication No. 2003-332885, for example, a duplexer having a circuit configuration shown in FIG. 8 is disclosed. As illustrated in FIG. 8, a duplexer 1001 includes a reception side band-pass filter 1002 and a transmission side band-pass filter 1003 for a cellular phone. The reception side band-pass filter 1002 is a ladder filter including series-arm resonators S101 to S103 and parallel-arm resonators P101 and P102.
The transmission side band-pass filter 1003 is a ladder filter including series-arm resonators S111 to S113 and parallel-arm resonators P111 and P112. The reception side band-pass filter 1002 and the transmission side band-pass filter 1003 are each defined by an elastic wave filter chip. One end of the reception side band-pass filter 1002 and one end of the transmission side band-pass filter 1003 are commonly connected to a node 1004. The node 1004 is connected to an antenna 1006 through an inductance element 1005. In addition, a capacitor 1007 is connected between a node between the antenna 1006 and the inductance element 1005 and a ground potential.
In the reception side band-pass filter 1002, an inductance element 1008 is connected in parallel with the series-arm resonator 103. In contrast, in the transmission side band-pass filter 1003, an inductance element 1009 is connected in parallel with the series-arm resonator S112.
The duplexer 1001 includes an input terminal 1001a connected to the antenna 1006, a reception terminal 1001b, and a transmission terminal 1001c. 
FIG. 9 is a schematic front sectional view illustrating a specific structure of the duplexer 1001.
In the duplexer 1001, the reception side band-pass filter 1002 defined by the elastic wave filter chip is mounted on a laminated substrate 1011 by a flip-chip bonding method using bumps 1012 and 1013. A coil pattern 1008a of the inductance element 1008 is provided in the laminated substrate 1011.
On the other hand, FIG. 10 is a sectional plan view schematically illustrating the electrode structure in the laminated substrate 1011 at a height level at which the inductance element 1008 is provided. The coil pattern 1008a and a coil pattern 1009a of the inductance elements 1008 and 1009, respectively, are provided in a plane at this height level. Coil patterns 1008b and 1009b are provided at a height level different from that at which the coil patterns 1008a and 1009a are provided. The coil pattern 1008a and the coil pattern 1008b are connected by a via-hole conductor. The coil patterns 1009a and 1009b are connected by a via-hole conductor. The inductance element 1005 and the capacitor 1007 are provided outside of the laminated substrate as external elements.
In a duplexer 1001 described in Japanese Unexamined Patent Application Publication No. 2003-332885, a plurality of inductance elements 1008 and 1009 are included in a laminated substrate 1011. Therefore, the size of the duplexer 1001 is reduced by mounting a reception side band-pass filter 1002 and a transmission side band-pass filter 1003, both of which are defined by elastic wave filter chips, by a flip-chip bonding method.
However, it is desirable for the size of an electronic component for a cellular phone, such as the duplexer 1001, to be further reduced, especially in thickness. When an inductor is included in a laminated substrate, a larger inductance can be obtained by, for example, electrically connecting a plurality of coil patterns provided at a plurality of height levels using a via-hole conductor and thereby increasing the number of turns of the coil patterns. However, when coil patterns are formed at a plurality of height levels, the thickness of the laminated substrate increases, making it difficult to reduce the thickness thereof.